Large-scale, worldwide adaptive radiations have occurred in which of the following situations?
a. When there are no available ecological niches
b. After each of the big five mass extinctions
c. Aafter colonization of an isolated island that contains suitable habitat and few competitor species
d. Whenever an evolutionary innovation was needed for organisms to thrive

Verified step by step guidance

1. Understand the concept of adaptive radiation: Adaptive radiation refers to the rapid evolution of diverse species from a common ancestor when new ecological opportunities arise. This often happens when organisms encounter environments with unoccupied niches or reduced competition.
2. Analyze the role of ecological niches: Adaptive radiation typically occurs when ecological niches are available, allowing species to diversify and adapt to different roles in the ecosystem. This eliminates option 'a' since adaptive radiation does not occur when there are no available niches.
3. Examine the impact of mass extinctions: Mass extinctions create opportunities for adaptive radiation by eliminating dominant species, freeing up ecological niches for surviving organisms to diversify. This supports option 'b' as a correct scenario.
4. Consider colonization of isolated islands: When species colonize isolated islands with suitable habitats and few competitors, they often undergo adaptive radiation to exploit the available niches. This supports option 'c' as another correct scenario.
5. Evaluate evolutionary innovations: While evolutionary innovations can help organisms thrive, they are not a direct cause of adaptive radiation. Adaptive radiation is more closely tied to ecological opportunities rather than the need for innovation, making option 'd' less relevant.

Key Concepts

Adaptive Radiation

Adaptive radiation is an evolutionary process where organisms diversify rapidly into a wide variety of forms to adapt to different environments. This often occurs when a species colonizes a new habitat with available ecological niches, leading to the emergence of new species that exploit these niches. Understanding this concept is crucial for analyzing how and why large-scale radiations happen in response to environmental changes.

Mass Extinctions

Mass extinctions are significant and rapid decreases in biodiversity on Earth, often resulting from catastrophic events such as asteroid impacts or volcanic eruptions. The five major mass extinctions in Earth's history have led to the loss of a large number of species, but they also create opportunities for surviving species to diversify and fill the vacated ecological niches, often resulting in adaptive radiations.

Ecological Niches

An ecological niche refers to the role and position a species has in its environment, including its habitat, resource use, and interactions with other organisms. The availability of ecological niches is a key factor in adaptive radiation, as it allows new species to evolve and thrive in different environments. Understanding niches helps explain why certain events, like mass extinctions or colonization of isolated areas, can trigger rapid diversification.